IAG Planetary Geomorphology Working Group

A large canyon system (up to 8 km deep) called Valles Marineris is located near the equator on Mars. The relative timing between the formation of the Valles Marineris canyon system and various light-toned stratified deposits observed within the different chasmata remains an outstanding question for the geologic history of Mars (Malin and Edgett 2000; Okubo et al. 2008) . Some of these stratified deposits have been deformed and understanding the mechanism(s) responsible for this deformation, both within and between chasmata, could provide insight into the relative timing of events within the Valles Marineris system (Metz et al. 2010).

Deformation of sedimentary rocks is widespread within Valles Marineris and observed styles of deformation include detached slabs which are rounded blocks of detached material that only locally shows evidence of layering. These slabs in Image 1 are inferred to be composed of sedimentary rocks, and they contain finely stratified deposits with the spectroscopic signature of evaporite minerals. Kilometer-scale convolute folds are similar to detached slabs, but they are composed of alternating dark and light toned strata that exhibit disharmonic folding (Image 2). Folded strata exhibit many geometries including similar and concentric folds, domes, basins, crescents, mushrooms and other interference patterns (Image 3). Pull-apart structures are areas that show evidence of possible brittle deformation and appear to be composed of fragments of strata that have broken off into small irregularly shaped pieces. In some areas the fragmented strata look as if they could be fit back together similar to puzzle pieces, whereas in other areas the fragmentation proceeded to a larger degree and only irregularly shaped fragments of strata remain (Image 4).